Explosive and method of manufacture thereof



Patented Sept. 20, 1938 EXPLOSIVE AND METHOD OF MANUFAC- TUBE THEREOFRobert W. Cairns, Wilmington, Del., assignor to Hercules Powder Company,Wilmington, Del., a corporation of Delaware No Drawing. Application May11,1936, Serial No. 79,180

13 Claims.

This invention relates to a new and improved explosive and method ofmanufacture thereof, and more specifically to a new and improvedexplosive containing ammonium nitrate of innitrate have suffered fromthe disadvantage of insensitivity to detonation, and require about 10%of their composition to be nitroglycerin, nitroglycol," or the like, toimpart sufficient sensitiveness to detonation to enable such dynamitesto be detonated by the usual No. 6 blasting cap or to propagateexplosion from one cartridge to the next when in a borehole.

Ammonium nitrate alone, while capable of detonation by anextraordinarily high initial shock or impulse, is unsuitable by itselffor commercial explosives, because it is too insensitive to detonationby the means ordinarily employed, and also because it will not propagateexplosion from one cartridge to the next when in a borehole.

In addition to the ordinary means of increasing the sensitiveness ofhigh ammonium nitrate mixtures, i. e., admixture of nitroglycerin andthe like, various attempts have been made to increase the sensitivenessto detonation of ammonium nitrate by other'means, but none of these aresatisfactory or have achieved commercial application. For example,alkali metal nitrates, particularly sodium nitrate and potassiumnitrate, have been used extensively in explosive compositions, primarilyon account of their cheapness and the fact that such mixtures withcarbonaceous materials are effective absorbents for liquid explosivesand, at the same time, contribute energy to the explosion. U. S. Patent1,568,324 discloses a process of manufacture of conglomerate masses ofammonium nitrate and sodium nitrate for explosive purposes, whichcomprises partial or complete fusion of the dry salts, rapid cooling ofthe melt, and pulverizing the product." The use of water to make theabove mixture is excluded, because the masses were difficult to dry andhopelessly insensitive to detonation. I

My invention involves broadly coating a metal nitrate on ammoniumnitrate crystals preferably without substantial alteration of the shapeor size of the ammonium nitrate crystals, and the prod uct obtainedthereby. I thereby obtain an ammonium nitrate of highly increasedsensitiveness to detonation, capable of incorporation with othersubstances normally used in dynamites, or, if nitroaromatic compounds orlike sensitizers commonly used in explosives, be added, with the use ofsmaller amounts of such sensitizer than here- 5 tofore found necessary.

Wholly contrary to expectation, I have found that my sensitization ofammonium nitrate crystals by coating with a metal nitrate is effectivein connection with the use of added sensitizers having a large negativeoxygen balance, e. g., organic nitrocompounds, such as thenitrotoluenes, nitroxylenes, nitronaphthalenes, etc., ordiethyleneglycol dinitrate, but is not effective with sensitizers havinga low oxygen deficiency or an oxygen excess, e. g., nitroglycerin,nitroglycol, nitrolactose, and the like. However, I may use the latter,if desired, in combination with oxygen-deficient organic nitrocompounds,if the oxygendeficiency of the mixture be great. I am unable to give areason for this effect, but state it as a fact found by lengthyexperiment.

, Contrary to prior art, I have found, much to my surprise, that I mayuse aqueous solutions of metal nitrates to deposit crystals of metalnitrates.on ammonium nitrate to increase the sensitiveness to detonationof the latter, and I find the use of water, as the solvent for metalnitrates applied to ammonium nitrate crystals, highly desirable, sinceit affords a substantial increase in the safety of the operation byreducing the temperature required to bring the metal nitrate into propercontact with the ammonium nitrate.

As a specific example of the process in accordance with my invention Iprepare a solution by dissolving 132 parts by weight of ammonium nitrateand 50 parts by weight of sodium nitrate in 66 parts by weight of waterat about 27 C. This solution is saturated with respect to ammoniumnitrate and almost saturated with sodium nitrate.

This solution is applied at 27 C.

Jcontinuous stirring. After. 3-4 hours,the moisture content is less than0.2%.

u Similarly, I may use as thecoating solution a water solution ofammonium nitrate and nitrate of copper, lead, zinc, potassium, cadmium,nickel,

or any metallic nitrate.

I prefer to have such coating solution saturated with respect toammonium nitrate, so that it will exert a minimum 1 of solvent actionupon the ammonium nitrate grains with which it comes in contact, altho Ido not so limit myself. For example, the coating solution may contain noammonium nitrate, or may contain less than the amount required forsaturation. In this event, some of the ammonium nitrate crystals towhich the solution is applied will be partly dissolved, but thecoatingsolution should preferably be of such volume and concentrationthat the greater part of the ammonium nitrate to which it is appliedremains undissolved.

I do not limit myself to drying the coated ammonium nitrate crystals bypassing air therethrough, but the drying may be done by merely heatingthe coated crystals, and in such case I monium nitrate by determiningthe limiting density at which detonation is accomplished by a No. 6 or aNo. 8 blasting cap. In the following, the above method of determiningsensitiveness has been employed.

For the purpose of illustrating the increased sensitiveness todetonation of my coated ammonium nitrate, I prepared a series ofexplosives containing 92 parts by weight of screened ammonium nitrate,coated with about 5% of metal nitrates as heretofore described, 5 partsby weight of dinitrotoluene oil, and 3 parts by weight of ground softcoal. The explosive containing uncoated ammonium nitrate I designate, inthe following table, as A, that coated with sodium nitrate B, withcopper nitrate C, with lead nitrate D, with zinc nitrate E.

prefer to heat the coating solution before applying the same to theammonium nitrate crystals, to facilitate drying. I prefer to have thecoating solution almost saturated with the coating salt, to minimize theamount of water to be evaporated and to minimize the solvent action onthe ammonium nitrate crystals. I may apply the coating solution morethan once, to increase the amount of coating salt deposited on theammonium nitrate crystals.

I have found that it is unnecessary to have the ammonium nitratecrystals completely dry before application of the coating salts. Forexample, the ammonium nitrate crystals may contain enough adheringmoisture to dissolve the required amount of metal nitrate, which lattermay then be added in a dry state, stirred until dissolved by theadhering mother liquor, and the mixture then dried.

I may disperse or dissolve carbonaceous or organic sensitizingingredients in the coating solutions. Such may be clone 'safely attemperatures below C., but would be very dangerous if the sensitizingagents were added to the ammonium nitrate crystals by a fusion process,e. g., according to the proceg disclosed in U. S. Patent 1,568,324.

To determine the sensitiveness and efficiency of explosives made fromammonium nitrate sensitized according to my improved process, I preferto use the small lead block compression test as described in U. S.Bureau of Mines, Bulletin No. 346, pages 106-108, 1931 edition. In thistest, a short column of the explosive (100 grams) at the desired densityis placed on top of a vertical, lead cylinder 1.5 inches in diameter and2.5 inches high, capped with a steel disc M inch thick. The explosive isdetonated by a blasting cap, the detonation drives down the steel discand compresses the lead cylinder by an amount commensurate with thevelocity of detonation and completeness .of detonation of the explosive.Since an increase in the density of loading of an explosive markedlydesensitizes ammonium nitrate explosives, it is possible to estimate thesensitization produced by the coating on the am- Comparison of thesensitiveness to No. 6 or No. 8 blasting caps of composition A, withcompositions B to E shows clearly the advantages in sensitiveness todetonation gained by coating the ammonium nitrate with various metalnitrates. Although not shown in the table, similar increases insensitiveness were obtained with coatings of nitrates of potassium,cadmium, nickel, iron, calcium and magnesium.

To illustrate the improvement in sensitiveness to detonationaccomplished by my coating process, as compared to mixtures of ammoniumnitrate and a metal salt, an explosive was made up on the samecomposition as B, in Table I, but with the sodium nitrate added dry tothe ammonium nitrate, after screening through a 100 mesh screen. Thisexplosive composition detonated partially with a No. 6 blasting cap at adensity of 1.02 g./cc.,. and failed to detonate with a No. 8 blastingcap at a density of 1.08 g./cc. Furthermore, in this explosive, thepresence of the fine sodium nitrate caused greatly increased setting"difficulties, i. greatly increased caking or hardening of the explosiveduring storage.

The amounts and kind of metal nitrate applied as coating on the ammoniumnitrate determines the degree of sensitization to detonation of, theammonium nitrate. For example, an explosive made up on the same generalcomposition as explosive E in Table I, except that only 1% of zincnitrate coating was on the ammonium nitrate, had a limiting density of1.02 g./cc. for a No. 6 blasting cap.

Although, in the foregoing, I have illustrated only dinitrotoluene oiland coal as the sensitizing agents to add to my sensitized ammoniumnitrate to produce a commercial explosive, I may use other carbonaceousingredients than coal, e. g., charcoal, corn meal, flour, wood pulp,etc., and in place of the dinitrotoluene oil I may use soliddinitrotoluene, trinitrotoluene, dinitronaphthalene, and other liquidand solid nitro-compounds, incorporated by the use of heat, for examplein amounts depending upon the type of dynamite and on the sensitivenessrequirements of the trade.

What I claim and desire to protect by Letters Patent is:

1. The method of increasing the sensitiveness to detonation of ammoniumnitrate comprising adding to ammonium nitrate crystals a solution todetonation of ammonium nitrate comprising adding to ammonium nitratecrystals a metal nitrate solution saturated with ammonium nitrate, anddrying the mixture.

4. An explosive composition sensitive to detonation comprising ammoniumnitrate particles coated with a metal nitrate.

5. An explosive composition sensitive to detonation comprising ammoniumnitrate crystals coated with crystals of a metal nitrate.

6. An explosive composition comprising ammonium nitrate crystals coatedwith crystals of a metal nitrate, and an organic sensitizer having ahigh oxygen deficiency.

7. An explosive composition comprising ammonium nitrate crystals coatedwith crystals of a metal nitrate, an organic sensitizer having a highoxygen deficiency, and a carbonaceous ingredient.

8. An explosive composition comprising trinitrotoluene, a carbonaceousingredient, and ammonium nitrate crystals coated with crystals of ametal nitrate.

9. An explosive composition comprising nitronaphthalene, a carbonaceousingredient, and ammonium nitrate crystals coated with crystals of ametal nitrate.

10. An explosive composition comprising a carbonaceous ingredient,dinitrotoluene, and a1..- monium nitrate crystals coated with crystalsof a metal nitrate.

11. An explosive composition comprising a carbonaceous ingredient,dinitrotoluene, and ammonium nitrate crystals coated with crystals ofzinc nitrate.

12 An explosive composition comprising ammonium nitrate crystals coatedwith crystals of calciumnitrate, a carbonaceous ingredient, anddinitrotoluene.

13. An explosive composition comprising a carbonaceous ingredient,dinitrotoluene, and ammonium nitrate crystals coated with crystals ofmagnesium nitrate.

ROBERT W. CAIRNS.

